These are the same settings the platform UI shows in the Reddit section of the
            campaign draft page. The campaign MUST already have its Reddit channel enabled
            (via create_campaign / add_and_edit_campaign_elements with a `reddit` block).

            WARNING: DRAFT-ONLY: the platform rejects these edits once the campaign is Launching/Launched.

            KEYWORDS: reddit, reddit campaign, reddit settings, campaign settings, draft campaign,
            objective, native objective, traffic, brand awareness, reach, views, video views, video views 6s,
            impressions, clicks, comments, allow comments, placements, placement, feed, conversations,
            pixel, conversion pixel, conversion tracking, bid, bid amount, manual bid, auto bid, settings

            WHEN TO USE:
            - Change the Reddit objective (e.g. from Brand Awareness to Traffic)
            - Toggle "Allow comments" on Reddit ads
            - Select placements (Feed and/or Conversations)
            - Attach or clear a Reddit conversion pixel
            - Set a manual bid amount for Brand Awareness / Video Views objectives

            PARAMETERS (campaign_id required; everything else optional — unspecified
            settings keep their current values on the channel):
            - campaign_id: the wizard campaign ID
            - objective: IMPRESSIONS (Brand awareness and Reach) | CLICKS (Traffic) |
              VIDEO_VIEWABLE_IMPRESSIONS_6S (Video Views 6s). Mirrors the platform UI's
              Native Objective dropdown.
              WARNING: Lead Gen (CPL) campaigns only accept CLICKS (landing pages require it).
              WARNING: Video Views requires the channel to contain ONLY video ads.
            - allow_comments: whether Redditors can comment on the promoted post (platform default: true)
            - placements: {"feed": bool, "conversations": bool}. At least one must stay
              selected (Feed wins if both are false). Conversations is forced OFF when the
              channel has video ads.
            - conversion_pixel_id: pixel id from the account's Reddit Ads Manager. Pass an
              empty string "" to clear. Pixels are managed in Reddit Ads Manager, not here.
            - bid_amount: manual bid amount. Only applied when the effective objective uses
              MANUAL_BID (IMPRESSIONS / Video Views). Ignored for CLICKS (AUTO_BID).

            BID STRATEGY (automatic): changing the objective re-applies the UI's auto-switch —
            CLICKS → AUTO_BID; IMPRESSIONS / VIDEO_VIEWABLE_IMPRESSIONS_6S → MANUAL_BID.
            The bid strategy is left untouched when neither objective nor bid_amount is sent.

            EXAMPLES:

            Switch a Brand Awareness campaign's Reddit channel to Traffic:
            update_reddit_channel_settings({"campaign_id": 12345, "objective": "CLICKS"})

            Disable comments and run Feed-only:
            update_reddit_channel_settings({
                "campaign_id": 12345,
                "allow_comments": false,
                "placements": {"feed": true, "conversations": false}
            })

            Brand awareness with a manual bid and a conversion pixel:
            update_reddit_channel_settings({
                "campaign_id": 12345,
                "objective": "IMPRESSIONS",
                "bid_amount": 1.5,
                "conversion_pixel_id": "pixel_abc123"
            })

            RESPONSE: {success, campaign_id, channel_id, campaign_status, applied:{...}, errors?}
            `applied` echoes exactly what was pushed to the platform.

            INTEGRATION WITH OTHER TOOLS:
            - Use search_campaigns_by_names / get_campaign_by_wizard_id to find the campaign
            - Reddit channel is enabled by create_campaign or add_and_edit_campaign_elements
            - Reddit ads come from create_update_image_ad / create_update_video_ad with channels=["REDDIT"]